!!! Highly Recommend printing the ThreadTest ring to make sure your printer and settings are dialed in properly for printing threads and accurate dimensions. My printer is calibrated precisely on all axis with no expansion settings in my slicer, so this came out perfect, YMMV.
I used a variable resolution set at 0.2 for layer height, with steps and maximum deviation of 0.04mm. You could probably print the whole model in 0.2mm and it would be just fine, I just wanted my threads to fit really nicely since they are sharp, and the top to not droop as much (which worked very well!)
My print is a nice and snug fit so I could just screw it on as far as I needed to set rotation, if you cant quite get it snug so as not to rotate, you can use the ThreadTest as a jam nut to hold it's position.
If you want to be sure the threads print properly, and the top doesn't sag too much, print using 0.16mm layer height.
Since this will be an outdoor installation, I highly recommend PETG or something similar in properties to stand up against high water pressure, UV, and occasionally getting bumped around in the pool.
In the future, I am looking to make a low-profile version, that won't create much backpressure and will stick out less than this one, but for the time being, this works great!
Amazon Basics Orange PETG, 10% Gryoid infill, variable 0.16-0.24mm layer height